Anaplastic lymphoma kinase (ALK) is a member of the receptor tyrosine kinase superfamily, and at an amino acid sequence level is most closely related to members such as Ros-1, leucocyte tyrosine kinase, the insulin receptor and cMet (hepatic growth factor receptor) (Kostich M et al, Genome Biology, 2002, 3, 1-12). As with all members of this gene family, it possesses an extracellular ligand binding domain, a transmembrane spanning sequence, and an intracellular kinase catalytic region/signalling domain. The identity of the signalling ligand for ALK is not yet elucidated and different mechanisms have been proposed in the literature (Stoica G. E. et al., J. Biol. Chem., 2001, 276, 16772-16779; Stoica G. E. et al., J. Biol. Chem., 2002, 277, 35990-35999; Mewng K. et al., PNAS, 2000, 97, 2603-2608; Perez-Pinera P. et al., J. Biol. Chem., 2007, 282, 28683-28690). The stimulation of ALK leads to an intracellular signalling cascade via phopholipase-C, PI3Kinase and STAT3 (amongst other signalling proteins) (Turner S. D. et al., Cell Signal, 2007, 19, 740-747).
ALK is largely expressed in the developing nervous system (Iwahara T. et al., Oncogene, 1997, 14, 439-449). Its relative abundance does tend to decrease in the adult animal, though its expression is maintained in certain regions of the brain, spinal cord and the eye (Vernersson E. et al., Gene Expression Patterns, 2006, 6, 448-461).
ALK has an important role in oncology (Webb T. R. et al., Expert Reviews in Anticancer Therapy, 2009 9 331-355). Point mutations in the full length ALK enzyme that lead to activation of the enzyme, and also increase in expression of the full length enzyme, have both been shown to lead to neuroblastoma. In addition, the fusion of ALK with other proteins due to genetic translocation events has also been shown to lead to activated kinase domain associated with cancer. A number of such ALK translocations leading to gene fusions are seen in lymphomas, the most prevalent being the nucleophosmin NPM-ALK fusion seen in anaplastic large cell lymphomas. ALK fusion with EML4 leads to a chimeric protein (EML4-ALK) thought to be responsible for a 3-5% of non small cell lung adenocarcinomas (NSCLC) (Soda M. et al., Nature, 2007, 448, 561-567).
Crizotinib is a potent dual tyrosine kinase inhibitor (TKI) targeting c-Met and ALK that has recently found application in the treatment of NSCLC patients harbouring the EML4-ALK fusion event (Kwak et al., New Eng. J. of Med., 2010, 363, 18, 1693-1703). Crizotinib is disclosed in PCT Publication No. WO 2006/021884 and U.S. Pat. No. 7,858,643. Acquired resistance to crizotinib therapy has be reported and attributed to a L1196M and a C1156Y mutation in the EL4-ALK fusion protein (Choi Y. L. et al., N. Engl. J. Med., 2010, 363, 18, 1734-1739). As crizotinib therapy becomes more widely available to patients harbouring the EML4-ALK gene fusion event, it is likely that the L1196M and C1156Y mutations and possibly other mutations will play a more prevalent role in acquired resistance to crizotinib therapy. See, e.g., Morris et al. United States Patent Publication Number 2011/0256546 describing other ALK inhibitor resistance mutations occurring in the ALK kinase domain of the related gene fusion NPM-ALK).
Accordingly, there is a need for ALK inhibitors and EML4-ALK inhibitors that have an appropriate pharmacological profile, for example in terms of potency, selectivity, pharmacokinetics, ability to cross the blood brain barrier and duration of action. More specifically, there is a need for ALK inhibitors that inhibit the EML4-ALK fusion protein having a L1196M and/or C1156Y mutation. In this context, the present invention relates to novel ALK inhibitors.